U.S. patent number 8,841,152 [Application Number 13/465,065] was granted by the patent office on 2014-09-23 for method of lift-off patterning thin films in situ employing phase change resists.
This patent grant is currently assigned to Massachusetts Institute of Technology. The grantee listed for this patent is Matthias Erhard Bahlke, Marc A. Baldo, Hiroshi Antonio Mendoza. Invention is credited to Matthias Erhard Bahlke, Marc A. Baldo, Hiroshi Antonio Mendoza.
United States Patent |
8,841,152 |
Bahlke , et al. |
September 23, 2014 |
**Please see images for:
( Certificate of Correction ) ** |
Method of lift-off patterning thin films in situ employing phase
change resists
Abstract
Method for making a patterned thin film of an organic
semiconductor. The method includes condensing a resist gas into a
solid film onto a substrate cooled to a temperature below the
condensation point of the resist gas. The condensed solid film is
heated selectively with a patterned stamp to cause local direct
sublimation from solid to vapor of selected portions of the solid
film thereby creating a patterned resist film. An organic
semiconductor film is coated on the patterned resist film and the
patterned resist film is heated to cause it to sublime away and to
lift off because of the phase change.
Inventors: |
Bahlke; Matthias Erhard
(Cambridge, MA), Baldo; Marc A. (Lexington, MA), Mendoza;
Hiroshi Antonio (Cambridge, MA) |
Applicant: |
Name |
City |
State |
Country |
Type |
Bahlke; Matthias Erhard
Baldo; Marc A.
Mendoza; Hiroshi Antonio |
Cambridge
Lexington
Cambridge |
MA
MA
MA |
US
US
US |
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Assignee: |
Massachusetts Institute of
Technology (Cambridge, MA)
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Family
ID: |
47175215 |
Appl.
No.: |
13/465,065 |
Filed: |
May 7, 2012 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20120295382 A1 |
Nov 22, 2012 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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61487839 |
May 19, 2011 |
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Current U.S.
Class: |
438/39; 438/715;
257/E21.349 |
Current CPC
Class: |
H01L
51/0016 (20130101) |
Current International
Class: |
H01L
21/00 (20060101); H01L 21/302 (20060101); H01L
21/461 (20060101) |
Field of
Search: |
;438/39,82,715
;216/40,73 ;257/E21.349 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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4318663 |
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Oct 1994 |
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DE |
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0233747 |
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Aug 1987 |
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EP |
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01-39986 |
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Jun 2001 |
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WO |
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Other References
IBM Tech. Disci. Bull. NA920675, "Selective Deposition with "Dry"
Vaporizable Lift-Off Mask". vol. 35, Issue 1A, (Jun. 1, 1002), pp.
75-76. cited by examiner .
IBM Tech. Disci. Bull. NA920675 (Jun. 1992) pp. 75-76. cited by
examiner .
IBM Tech. Disci. Bull. vol. 20, No. 9,(Feb. 1978). pp. 3737-3738.
cited by examiner .
The International Search report and Written Opinion issued in
Connection with International Patent Application No.
PCT/US2012/036870 mailed on Nov. 30, 2012. cited by applicant .
Selective Deposition With "Dry" Vaporizable Lift-off Mask, IBM
Technical Disclosure Bulletin, vol. 35, No. 1A, pp. 75-76, Jun.
1992. cited by applicant .
Condensed Gas, In Situ Lithography, IBM Technical Disclosure
Bulletin, vol. 20, No. 9, pp. 3737-3738, Feb. 1978. cited by
applicant.
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Primary Examiner: Everhart; Caridad
Attorney, Agent or Firm: Pasternack; Sam MIT Technology
Licensing Office
Government Interests
This invention was made with government support under Grant No,
DE-SC00G1088, awarded by the Department of Energy. The government
has certain rights in this invention.
Parent Case Text
This application claims priority to provisional application Ser.
No. 61/487839 filed on May 19, 2011, the contents of which are
incorporated herein by reference.
Claims
What is claimed is:
1. Method for making a patterned thin film of an organic
semiconductor for use in an electrical device structure comprising:
condensing a resist gas into a solid film onto a substrate selected
from the group consisting of glass, metal foil, polymer foil or
ceramic cooled to a temperature below the condensation point of the
resist gas; compressing the resist subsequent to condensation by
application of force to achieve a selected density; selectively
heating by laser light, resistive heating or by thermal contact
with raised features on a stamp the condensed solid film to cause
local direct sublimation from solid to vapor of selected portions
of the solid film thereby creating a patterned resist film with
feature dimensions of five micrometers or larger; coating an
organic semiconductor film on the patterned resist film; and
heating the patterned resist film to cause it to sublime away and
to lift off because of the phase change.
2. Method for making a patterned organic film that can be used in a
light-emitting diode (OLED) comprising: condensing a resist gas
into a solid film onto a substrate cooled to a temperature below
the condensation point of the resist gas; compressing the resist
subsequent to condensation by application of force to achieve a
selected density; selectively heating by laser light, resistive
heating or by thermal contact with raised features on a stamp the
condensed solid film to cause local direct sublimation from solid
to vapor of selected portions of the solid film thereby creating a
patterned resist film with feature dimensions of five micrometers
or larger; coating an organic film that can be part of a
light-emitting diode on the patterned resist film; and heating the
patterned resist film to cause it to sublime away and to lift off
because of the phase change.
3. The method of claim 1 or claim 2 wherein the resist gas is
selected from the group consisting of carbon dioxide, nitrous
oxide, argon, xenon, hydrogen chloride, acetylene, hexafluorethane,
butane, ethanol, ammonia, sulfur dioxide, isobutane, ethylene,
chloroform, formic acid, iodine, and uranium hexafluoride.
4. The method of claim 1 or claim 2 wherein condensation rate is
monitored.
5. The method of claim 1 or claim 2 wherein heating the condensed
solid film is achieved by joule heating of resistive elements.
6. The method of claim 1 or claim 2 wherein heating is achieved by
optical patterning.
7. The method of claim 1 or claim 2 wherein the resist gas is
carbon dioxide and is patterned by a laser operating at 225, 2700
or 4300 nanometers.
8. The method of claim 1 or claim 2 further including an optically
dense guest material doped into the resist film during
condensation.
9. The method of claim 1 or claim 2 wherein resist patterning is
performed in vacuo or in an inert gas or gases.
10. The method of claim 1 or claim 2 used for making OLED
materials.
11. The method of claim 1 or claim 2 wherein resist lift-off is
effected by increasing the temperature of the condensate resist
across its sublimation point in pressure-temperature space.
12. The method of claim 1 or claim 2 wherein the lift-off is
effected by a thermal shock.
13. The method of claim 1 or claim 2 wherein two condensate resist
gases are used for film patterning, the thermal expansion
coefficients of the two gases differing by at least 5%.
14. The method of claim 1 or claim 2 wherein the substrate is
cooled to a temperature below the condensation point of the resist
gas.
15. The method of claim 4 wherein the substrate is cooled by
thermal conduction.
16. The method of claim 1 wherein the heating is achieved with a
patterned stamp such as a roller.
17. The method of claim 16 wherein the stamp is patterned by
chemical etching, mechanical scribing or direct laser ablation.
Description
BACKGROUND OF THE INVENTION
This invention relates to the patterning of metallic, insulator,
and semiconductor thin films by controlled removal for use in large
area electronics.
The production of large area electronic devices utilizing organic
semiconductor films typically requires the spatial patterning of
various materials over a large area substrate. These films must
also possess precisely defined thicknesses to ensure device and
system functionality. Large area electronics typically utilize
non-semiconductor substrates such as glass, plastic, metal foil, or
ceramic and may be rigid or flexible. Such electronic devices are
utilized in a number of product applications, including displays,
lighting components, photovoltaics, sensors, and identification
tags. Displays may be utilized in a number of settings, including
televisions, mobile phones, signage, cameras, computers, global
positioning systems, and gaming devices. The organic semiconductor
films and ail layers that are deposited above them cannot be
patterned by photolithography, as common photosensitive resist
materials and associated solvents used in conventional electronics
that employ semiconductor substrates dissolve many of the organic
semiconductors that are desirably utilized.
As a result, patterning methods other than photolithography must be
utilized to manufacture devices which contain organic semiconductor
materials. Many of these methods have undesirable traits, which
result in high production costs, low device throughput, and low
production yield. Additionally, some methods may be restrictive in
their compatibility with some materials, resulting in the use of
alternative materials which may have performance traits that are
less desirable.
One method to manufacture devices which contain organic
semiconductor materials employs the use of fine metal masks with
physical vapor deposition. The large area mask must be aligned to
the underlying substrate prior to each deposition, which reduces
throughput. These masks may expand and contract during film
deposition, resulting in misalignment of film layers between device
components over the large area substrate. When large masks are used
to process large substrates, they may sag under their own weight,
resulting in device feature misalignment. Mask sagging may be
reduced with a vertical mask geometry, but this process may require
additional substrate handling and highly customized source delivery
systems, increasing production costs and reducing production
throughput. The masks must be cleaned and replaced periodically,
increasing production costs and reducing machine uptime.
Another method to manufacture devices which contain organic
semiconductor materials employs the use of printheads, which may
selectively deposit material over a small area. Large area
substrates may be selectively coated by scanning one or more
printheads. The printheads serially scan the substrate, resulting
in patterned films. The scanning process may be slow, reducing
process throughput. Using multiple printheads may increase the
deposition rate, but each printhead may differentially degrade in
deposition performance, resulting in functional non-uniformities
over the substrate area. Material delivery may be achieved by a
number of methods all of which dissolve desirably patterned
materials in a solvent. However, solvents may degrade performance
if they contribute impurities that do not evaporate away from the
substrate. If deposited in liquid form, the liquid may flow,
resulting in deposition non-uniformities. Substrates that, have
been patterned in a previous step to have physical wells or areas
of surface energy to increase deposition uniformity have been
utilized, but these methods may not be compatible with all
substrates and require additional processing steps, which may
increase manufacturing cost. Devices which require multiple
patterned films which cannot be deposited through the printhead in
a single step must utilize solvents in subsequent printing steps
which will not dissolve the already patterned films. Such
restrictions on solvent requirements may exclude the use of certain
materials to be desirably patterned and may require the use of more
expensive solvents, which may either degrade device performance or
increase production cost. If deposited in solid form through local
evaporation at the printhead, the printhead and substrate may have
to dissipate a large amount of thermal energy, reducing production
throughput and increasing cost. This process may also result in
device performance that is inferior to devices fabricated by
alternate means, such as fine metal masked physical vapor
deposition, resulting in undesired performance traits. Alternative
materials may be utilized that do not show a difference between the
two production processes, but these materials may not result in end
device performance that is superior to alternative patterning
methods.
Another method to manufacture devices which contain organic
semiconductor materials employs the use of materials that are
uniformly pre-coated on a secondary substrate which are then
selectively transferred to the production substrate by means of a
localized energy beam, such as a laser, which induces local
vaporization. The laser or optical steering components are scanned
over the secondary substrate, resulting in patterned films. This
process may also result in device performance that is inferior to
devices fabricated by alternate means, such as fine metal masked
physical vapor deposition, resulting in undesired product traits.
Alternative materials may be utilized that do not show a difference
between the two production processes, but these materials may not
result in end device performance that is superior to alternative
patterning methods. The scanning process may be slow, reducing
process throughput. Using multiple lasers or steering components
may increase the deposition rate, but each laser may differentially
fluctuate in intensity, resulting in deposition non-uniformities
and functional non-uniformities over the substrate area.
Another method to manufacture devices which contain organic
semiconductor materials employs the use of patterned cylinders for
selective deposition, such as offset lithography, rotogravure, and
relief printing. A pre-patterned cylinder is inked with the
desirably patterned material dissolved in a suitable solvent. The
cylinder is rolled over the substrate, resulting large areas of
patterned substrates. Cylinder transfer of inks requires the use of
solvents, which may degrade performance if they contribute
impurities that do not evaporate away from the substrate. On
certain substrates, the deposited ink may flow, resulting in
deposition non-uniformities. Substrates can have been patterned in
a previous step to have physical wells or areas of surface energy
to increase deposition uniformity, but these methods may not be
compatible with all substrates and require additional processing
steps, which may increase manufacturing cost. Devices which require
multiple patterned films which cannot be deposited by the cylinder
in a single step must utilize solvents in subsequent printing steps
which will not dissolve the already patterned films. Such
restrictions due to solvent requirements may exclude the use of
certain materials to be desirably patterned and may require the use
of more expensive solvents, which may either degrade device
performance or increase production cost.
Another method to manufacture devices which contain organic
semiconductor materials employs the use of specialized materials
which may be dissolved and deposited using solvents but whose
active material undergoes a photochemical reaction which renders
the material insolvent to solvents used in subsequent processing
steps. These specialized materials typically result in devices with
performance traits that are inferior to devices formed by alternate
means and materials, resulting in undesired product traits.
Another method to manufacture devices which contain organic
semiconductor materials employs the use of lasers to selectively
ablate material which has previously been blanket deposited through
some other means. This method may leave undesirable residues on the
substrate, contributing to reduced device performance.
U.S. Pat. No. 7,282,430 issued to Karg in 2007 discloses an
arrangement for patterning materials for use in large area
electronics. A functional material is liquefied under high pressure
and temperature in a chamber. The liquid is ejected through a
printhead controlled by, for instance, a piezo element. The ejected
liquid solidifies on a substrate through freezing which is
controlled to maintain a temperature lower than the temperature of
the liquid in the printhead. The printhead or substrate is serially
scanned, forming a pattern of solid material on the substrate. No
solvents are utilized in this process. Unlike the instant
invention, there is no resist material and no lift-off step in the
process. The instant invention is subtractive, where material is
selectively removed from the substrate unlike U.S. Pat. No.
7,282,430, which selectively adds material to the substrate. While
both the instant invention and U.S. Pat. No. 7,282,430 employ phase
change to result in selective patterning, U.S. Pat. No. 7,282,430
describes phase changes between liquid and solid, where the instant
invention describes phase changes between vapor and solid
phases.
In 1992, Cuomo disclosed a method to pattern films with a
vaporizable mask ("Selective Deposition With "Dry" Vaporizable
Lift-off Mask," IBM Technical Disclosure Bulletin, vol 35, No. 1A,
pp. 75-76, June 1992). A condensable vapor of either water,
acetone, or chlorobenzene is uniformly coated onto a substrate
forming a lift-off mask. The mask is spatially patterned with a
pulsed laser incident through a projection mask through selective
ablation. The substrate and patterned mask is uniformly coated with
a second material by sputtering or evaporation. The composite is
warmed by any of a variety of means to lift off the mask and
overlying material, transferring a pattern to the second material.
Unlike the instant invention, spatial patterning is communicated by
a pulsed laser incident through a projection mask. Projection masks
do not remedy deficiencies related to time consuming alignment
between a mask and the substrate. A lift-off mask comprised of
water, acetone, or chlorobenzene will dissolve certain materials
desirably used in large area electronic devices which utilize
organic semiconductors and do not have utility in patterning
elements of such devices.
In 1978, Johnson disclosed a method for in situ lithography
("Condensed Gas, In Situ Lithography," IBM Technical Disclosure
Bulletin, vol 20, No. 9, pp. 3737-3738, February 1978). A
condensable vapor is uniformly coated onto a wafer forming a
condensed gas resist (CGR). The CGR is spatially patterned using
local heat application from light beams (preferably lasers),
electron beams, or microwaves which are absorbed by the wafer, or
from lines on the wafer. The wafer and patterned CGR is uniformly
coated with a second material. The temperature of the entire wafer
is raised above the CGR boiling point, which serves to liquify the
CGR from its solidified state, which is followed by boiling to
remove both the CGR and the overlying material, transferring the
pattern in the CGR to the second material. Unlike the instant
invention, the process is intended for use with wafers.
Semiconductor wafers may be strongly absorptive of light beams,
providing a convenient means of selectively patterning the CGR. The
instant invention applies to non-semiconductor substrates such as
glass, plastic, metal foil, or ceramic which are suitable for large
area electronic devices for use in applications where semiconductor
substrates are too expensive for economically viable products. The
process employs two phase changes for resist lift-off, solid to
liquid and liquid to vapor, in contrast to the instant invention
which employs a single phase change from solid to vapor for resist
lift-off. Utilizing liquid boiling of the CGR diminishes the
achievable resolution of the desirably patterned film since the
liquid CGR will flow to some degree no matter how short the
residence time the CGR exists as a liquid. In addition, utilizing
liquid phase CGRs may increase residue formation on the substrate,
increase liquid surface tension effects and increase waste products
of the process.
U.S. Pat. No. 7,435,353 issued to Golovchenko in 2008 and U.S. Pat.
No. 7,524,431 issued to Branton in 2009 describe processes to form
high resolution patterned material layers on a structure. A vapor
is condensed to a solid condensate layer on a surface of the
structure and then selected nano-metrically patterned and
nano-scale regions of the condensate layer are locally removed by
directing electron beams at the selected regions, exposing the
structure at the selected regions. A material layer is then
deposited on top of the solid condensate layer and the exposed
structure at the selected regions. The solid condensate layer and
regions of the material layer that were deposited on the solid
condensate layer are then removed, leaving a patterned material
layer on the structure. The process is related to electron beam
lithography, where nano-scale patterns are transferred to a resist
for nano-scale electronic, mechanical and chemical devices. The
process employs either one scanned electron beam or multiple energy
beams to selectively pattern the condensate layer in contrast to
the instant invention, which utilizes either a single laser beam,
resistive heating from patterned line on the underlying substrate,
or a stamp with raised features brought into thermal contact with
the condensate layer. Due to the slow nature to electron beam
scanning, the processes described in U.S. Pat. Nos. 7,435,353 and
7,524,431 are applicable to nano-scale features and patterns and
are not readily scalable to larger feature sizes in excess of 5
micrometers in contrast to the instant invention, directed towards
the manufacture of large area electronic devices with features in
excess of 5 micrometers distributed over substrates with lateral
dimensions from 100 to 3000 centimeters in length or width.
U.S. Pat. No. 7,759,609 issued to Asscher in 2010 describes a
method for forming nano-patterns of a material on a substrate
called buffer layer assisted laser patterning. A layered structure
is formed on the substrate, this layered structure being in the
form of spaced-apart regions of the substrate defined by the
pattern to be formed, each region including a weakly physisorbed
buffer layer and a layer of the material to be patterned on top of
the buffer layer. A thermal process is then applied to the layered
structure to remove the remaining buffer layer in said regions, and
thus form a stable pattern of said material on the substrate
resulting from the buffer layer assisted laser patterning. The
method may utilize either positive or negative lithography. The
patterning may be implemented using irradiation with a single
uniform laser pulse via a standard mask used for optical
lithography. The positive lithography process utilizes laser pulsed
patterning of the composite of buffer (resist) and overlying
material which is deposited via soft landing following laser
ablation of the buffer layer, in contrast to the instant invention
whereupon a patterned condensate resist is coated with uniform
material which is subsequently removed. The negative lithography
process utilizes pulsed laser radiation to pattern the buffer and
utilizes laser ablation to lift off the buffer, in contrast to the
instant intention which utilizes a thermal shock induced by
temperature change to lift off the resist material. The negative
lithography process described in U.S. Pat. No. 7,759,609 is suited
for forming narrow lines of less than 30 nanometers, in contrast to
the instant invention directed towards the manufacture of large
area electronics with feature sizes greater than 5000
nanometers,
German patent DE 4318663 C1 issued to Holdermann in 1994 describes
a process to form patterned films. Water ice forms a solid layer on
a semiconductor substrate and then regions of the water ice layer
are exposed to localized heating through various means, removing
the water ice at the selected regions. A desirably patterned film
is formed by either plating or etching the regions not covered in
water ice. The plating or etching is performed in a liquid solution
maintained below 0 C, such that the water ice does not melt or
vaporize. The solid water ice layer is then removed, leaving a
patterned material layer on the structure. The process described in
DE 4318663 C1 selectively etches or plates the desirably patterned
material in contrast to the instant invention, which utilizes
blanket deposition followed by a lift-off process step. The process
described in DE 4318663 C1 utilizes water ice and may include water
vapor and/or liquid water. The instant invention is directed
towards the use of non-water condensate resists for the patterning
of films comprised of materials which are sensitive and reactive to
water to the degree that water is desirably limited to levels much
less than 1 part per billion.
U.S. Pat. No. 4,535,023 issued to Whitlock in 1985 describes a
process to pattern a target for x-ray lasing. A substrate is placed
in a gaseous atmosphere of a second material held at a temperature
below the condensation point of the second material, such that the
second material forms a condensed film on the substrate. The film
is selectively heated using masked light beams to vaporize areas of
the condensed film. The condensed film is not removed but forms an
active component of the laser. The process described in U.S. Pat.
No. 4,535,023 is directed towards the fabrication of targets for
x-ray lasing made out of, for instance, sodium and neon. In
contrast, the instant invention is directed towards the fabrication
of large area electronics containing organic semiconductor films.
The process described in U.S. Pat. No. 4,535,023 utilizes a
patterned condensed film as an active device component which is not
followed by subsequent deposition steps, whereas in the instant
invention the condensed film functions as a sacrificial layer to
lift-off a subsequently uniformly deposited film.
European patent document EP 0233747 published by Woods in 1987
describes a process to apply a polymeric resist coating of high
molecular weight to a substrate. The process exposes a substrate to
a vapor of an anionically polymerizable monomer which then
polymerizes on the substrate, which then can be useful as a resist
coating in lithographic processes employing plasma or acid etching.
The process described in EP 0233747 relates to polymerizable
condensable materials, in contrast to the instant invention
directed towards simple molecular or elemental materials which do
not form polymers or undergo any chemical reactions following
condensation on the substrate. The process described in EP 0233747
utilizes a patterned resist as a blocking layer for a selective
etching process, whereas in the instant invention the condensed
film functions as a sacrificial layer to lift-off a subsequently
uniformly deposited film
U.S. Pat. No. 4,348,473 issued to Okumura in 1982 relates to a
method for the preparation of microelectronic device which
comprises a series of process steps performed on a substrate in a
single vacuum chamber. A substrate is coated with a monomer film
which is subsequently polymerized following the exposure to a light
or electron beam. The selectively polymerized film is then
uniformly heated to vaporize the monomer regions; the patterned
polymer is used as a resist during a subsequent etching step and
removed thereafter. The process described in U.S. Pat. No.
4,348,473 is directed toward polymerizable resist materials, in
contrast to the instant invention directed towards simple molecular
or elemental materials which do not form polymers or undergo any
chemical reactions following condensation on the substrate. The
process described in U.S. Pat. No. 4,348,473 utilizes a patterned
resist as a blocking layer for a selective etching process, whereas
in the instant invention the condensed film functions as a
sacrificial layer to lift off a subsequently uniformly deposited
film.
SUMMARY OF THE INVENTION
The present invention overcomes the deficiencies of the
aforementioned techniques by providing a method and apparatus for
depositing patterned thin films for use in large area electronics
which incorporate organic semiconductor films at low cost over
large areas that offer good uniformity, thickness control,
resolution, and high process throughput without being restrictive
to the type of material to be patterned.
In one aspect, the invention is a process called phase change
lithography wherein a resist film patterned by selective thermal
transfer induced local sublimation. A second film which is to be
patterned is uniformly coated above the patterned resist film. A
second uniform thermal energy transfer sublimes the resist film,
which additionally lifts off the second film, resulting in partial
or complete image transfer. The process may be repeated for each
film to be desirably patterned to transfer an image relative to
features in the substrate. One or more patterned films serve as
device components in an electronic device functioning as either an
organic light emitting diode (OLED) used in a display, an OLED for
general purpose lighting, an organic photovoltaic (OPV) device for
light-energy conversion, a large area circuit comprised of organic
thin film transistors for identification tags, or an electronic
device or system with an encapsulant to protect the device or
system from environmental exposure.
In particular, in one aspect, the method of the invention for
making a patterned thin film of an organic semiconductor for use in
an electrical device structure includes condensing a resist gas
into a solid film onto a substrate selected from the group
consisting of glass, metal foil, polymer foil or ceramic cooled to
a temperature below the condensation point of the resist gas. The
condensed solid film is selectively heated with a patterned stamp
to cause local direct sublimation from solid to vapor of selected
portions of the solid film thereby creating a patterned resist film
with feature dimensions of five micrometers or larger. An organic
semiconductor film is coated on the patterned resist film and the
patterned resist film is heated to cause it to sublime away and to
lift off because of the phase change.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a schematic illustration of an embodiment of the
invention disclosed herein.
FIG. 2 is a schematic illustration of another embodiment of the
invention in which rollers are used to compress the condensed
resist gas.
FIG. 3 is a schematic illustration of an embodiment of the
invention using a microfeatured stamp/roller to define a desired
pattern in a resist layer.
FIGS. 4A and B are schematic illustrations of an embodiment of the
invention in which an electrical current selectively sublimes parts
of the resist layer.
FIGS. 5A and B are schematic illustrations of an embodiment of the
invention using optical patterning to selectively sublime parts of
the resist layer.
FIGS. 6A and B are schematic illustrations of an embodiment of the
invention utilizing a microfeatured stamp to define parts of the
resist mask.
FIGS. 7A and B are schematic illustrations showing partial-depth
stamping leaving a uniform thickness burn-off to remove the
remainder of desired regions.
FIG. 8 is a schematic illustration of an embodiment of the
invention showing co-deposition of materials.
FIGS. 9A and B are schematic illustrations showing patterning of a
material by subliming an underlying resist mask.
FIG. 10 is an optical micrograph of a patterned sublimable mask of
carbon dioxide according to the invention.
FIG. 11 is an optical micrograph of a 100 .mu.m-wide silver line
patterned using a sublimable carbon dioxide mask.
FIG. 12 is an optical micrograph of an array of 20 .mu.m by 50
.mu.m subpixals of Alq3 produced by stamping a sublimable mask of
carbon dioxide.
FIG. 13 is a graph showing the electrical characteristic of a
functional organic light emitting diode fabricated using a carbon
dioxide sublimable mask in accordance with the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Resist materials which are suitable for phase change lithography
include those that directly transition between solid and vapor by
sublimation at temperature and pressure ranges that are suitable
for use in chamber processing equipment typically used in large
area electronic device manufacturing. These ranges include
approximately 80 to 300 K in temperature and 10.sup.-8 and 10.sup.3
Torr in pressure. The resist material is desirably chemically inert
to the materials that are desirably patterned and that exist on the
substrate to be patterned. The resist material should also possess
a sublimation temperature that is greater than 77 degrees Kelvin,
such that the resist will condense on substrates cooled by liquid
nitrogen, a common industrial process coolant.
Resist materials compatible with the instant invention include
carbon dioxide, nitrous oxide (or dinitrogen monoxide), argon,
xenon, hydrogen chloride, acetylene, hexafluoroethane, butane,
ethanol, ammonia, sulfur dioxide, isobutane, ethylene, chloroform,
formic acid, iodine, and uranium hexafluoride. These examples are
illustrative and not restrictive. Other materials are also
envisioned and may be used.
Phase change lithography utilizes resist materials which are not
chemically reactive with the materials which are desirably
patterned or any other materials on the substrate to be patterned.
In particular, organic semiconductor films are typically reactive
with water and most organic solvents; this reactivity precludes the
use of photolithographic techniques to form patterns in them. As
such, it is not contemplated to use water or other organic solvents
commonly used in semiconductor processing as resist materials for
phase change lithography.
Carbon dioxide is a prime example of a material that can be used in
the described process. It has a triple point of 216 K and 3885 Torr
and is chemically inert making it compatible with the
aforementioned process parameters. It is inexpensive, readily
available and has been used in a proof-of-concept investigation to
pattern both organic and metallic thin films as seen in the example
photographs.
With reference now to FIG. 1, a substrate 10 is cooled and resist
gas is flowed into a chamber 12. The resist gas condenses on the
substrate forming a solid layer 14. In particular, the resist is
coated onto the substrate 10 through condensation. Prior to resist
coating, the substrate 10 is cooled to a temperature below the
condensation point of the resist gas. The substrate is exposed to a
partial pressure of resist gas introduced to the condensation
chamber 12 through a controlled method, such as a mass flow
controller or bleed valve 16. Substrate 10 cooling may be achieved
by thermal conduction via the structure that supports the substrate
or to the whole condensation chamber 12, which is exposed to a
cooled liquid, such as liquid nitrogen. As the resist gas
encounters the cooled substrate 10 it condenses into the solid film
14 coating. The rate of condensation may be monitored by any
convenient and suitable means, such as quartz crystal monitors,
pressure monitoring, machine vision, or any combination of these
methods.
The solid structure of the condensate resist affects patterning
resolution, lift-off quality, and yield. Higher density resist
films generally exhibit superior traits, and can be used to form
patterns of higher resolution, result in patterned areas of more
uniform thickness, and result in a patterned substrate with higher
device yield. Some resist gases may condense in films with
densities that are lower than desired, resulting in inferior
patterning and resultant device traits.
As shown in FIG. 2, rollers 18 may be used to compress the resist
gas. In one embodiment, the resist, is compacted subsequent, to
condensation through the application of force. A large, cooled body
20, hereafter referred to as the compressor 20, with a uniform
surface may be pressed into contact with the substrate 10,
resulting in an applied force perpendicular to the film 14
thickness. This force may compress the resist film, increasing its
density. The compressor 20 may be cooled to a temperature at or
near the substrate 10 temperature to limit resist sublimation. The
compressor may have a large, uniform face, such that it is brought
into contact with the substrate to be patterned one time for each
resist compression process step. Alternately, the compressor 20 may
have a large area face which is smaller than the substrate to be
patterned. The compressor compacts a partial area of the resist
film and is then stepped until the whole of the to-be-patterned
area is compressed. Alternatively, the compressor 20 may have a
large curved area which is less than the area to be patterned such
as a cylindrical roller, so that the curved area of the stamp is
rolled over the substrate, such that contact between the compressor
and the substrate is maintained over the full resist compression
process. An additional support roller may be utilized to provide
counterbalanced force to limit substrate flexing.
Material compression through perpendicular force of a material
which is deposited by condensation is common in manufacturing, such
as dry ice manufacturing. Carbon dioxide gas condenses on dry ice
press in a form that resembles snow. A press rapidly oscillates to
compress the snow into dense blocks or pellets, which serves to
limit sublimation, increasing shelf life and facilitating
transportation.
In one embodiment, the condensate resist 14 may be increased in
temperature and pressure by following a predefined path through its
temperature-pressure phase diagram such that is passes through a
melting point, where the solid resist changes to a liquid resist.
The material is then redirected through another predefined path
through its temperature-pressure phase diagram such that is passes
through a melting point, where the liquid resist changes to a solid
resist. In this manner, the resulting solid resist film will have a
higher density than the initial resist film deposited by
condensation.
FIG. 3 shows a microfeatured stamp/roller 22 (top roller) that
defines a desired pattern in the resist layer 14. For use in
electronics, it is desirable that the patterned features have a
controllable resolution to meet specifications for functionality
and device density. Physical layout of insulating, conductive, and
or semiconductor thin films dictate active device area, directly
impacting overall performance metrics.
Condensate patterning is achieved through the transfer of features
from a design to the film through selective thermal energy
transfer. Thermal energy may be applied directly to the areas where
full condensate removal is desired. Alternatively, thermal energy
may be applied to an area larger or smaller than the area where
full condensate removal is desired, since thermal energy may be
transferred laterally through the substrate during or after the
thermal power source is removed. The underlying substrate to be
patterned may be uniform and unpatterned, or may possess features
patterned by previous process steps.
Direct application of thermal energy may be applied by any
convenient and suitable means, including those compatible with
patterning of large substrates up to three meters in length or
width. In all cases, thermal energy delivery is applied according
to a desired layout relative to underlying features on the
substrate. A number of patterning processes are compatible.
With reference to FIG. 4, current running through a transparent
conducting oxide 24 on part of the substrate 10 (4A) heats up
selectively subliming parts of the resist layer 14 (4B). In one
embodiment, thermal energy is applied by joule heating of resistive
elements in the underlying substrate. The resistive elements may be
defined prior to condensation through any convenient and suitable
means. For instance, electrodes for organic light emitting and
organic photovoltaic diodes may be comprised of a transparent,
doped tin oxide with features defined by photolithography. In
organic light emitting and organic photovoltaic diodes, the organic
thin films to be desirably patterned are deposited atop a substrate
which already possesses patterned tin oxide electrodes. Resistive
heating provides a convenient and suitable means to apply thermal
energy, since resistive features are typically present in the
substrate which is to be desirably selectively coated with an
insulating or semiconducting film. Current flow through the
resistive features may be temporally adjusted to directly control
the amount of thermal energy transferred to the condensate film,
resulting in the selective sublimation of condensate resist. Large
area electronic systems may be comprised of many identical
elements. For instance, an active matrix light emitting diode
display deposited on a Generation 4 glass substrate may be
comprised of several million each of identical red, green, and blue
subpixels. Each of these subpixels require patterned layers of
organic semiconductor thin films. Resistive heating is suited to
this application, since large areas may be patterned in a
two-dimensionally parallel process, facilitating high throughput
patterning. Alternatively, the application of current may be
applied serially, although the patterning throughput will
decrease.
Optical patterning can also be used (FIG. 5A) to heat the film and
selectively sublime parts 26 of the resist layer 14 (FIG. 5B). The
optical patterning may be either a projected or scanning broadband
or narrow-band light beam 30 (such as a laser) source 28. In
another embodiment, thermal energy is delivered to the solid
condensate resist through absorption of light energy delivered via
a pulsed or continuous wave laser. Light absorption results in the
promotion of free carriers to higher energy levels, which may
convert the excited electrical state to thermal energy, which is
transferred to the solid condensate resist and utilized for feature
patterning by resist sublimation. For ail materials of interest,
absorption strength varies by wavelength according to underlying
material properties. As such, the wavelength of laser excitation is
chosen such that sufficient light absorption is achieved to result
in resist sublimation. Correspondingly, the wavelength of laser
excitation depends on the condensate resist material to be
patterned. For instance, carbon dioxide is highly transparent
throughout the visible spectrum. Light absorption is stronger in
the ultraviolet and infrared spectra, so carbon dioxide may be
patterned by lasers at approximately 255, 2700, or 4300 nanometers.
For large area patterning, optical energy may be delivered serially
via scanning the laser using rotatable optical elements. The laser
used to transfer light energy to the solid condensate may be
aligned to the substrate and existing features by any convenient
and suitable method, including machine vision, and making reference
to fiducials, or readily referenced features on the underlying
substrate.
In another embodiment, thermal energy is delivered to the solid
condensate resist through absorption of light energy by an
optically dense guest material which is doped into the resist film
during condensation. Light energy is delivered via a pulsed or
continuous wave laser. The optically dense guest material is
selected for the purpose of light absorption. The guest material is
desirably a material which will not contaminate the electronic
device. In one example, the guest material is chosen to be the same
organic semiconductor which will be deposited onto the selectively
patterned condensate resist. The wavelength of laser excitation and
the doping ratio of guest material in the resist are chosen such
that sufficient light absorption is achieved to result in resist
sublimation. Correspondingly, the wavelength of laser excitation
depends on the guest material. For instance, aluminum
tris(quinolh-8-olate) (Alq3) strongly absorbs violet light at 400
nanometers. So a condensate resist doped with Alq3may be patterned
with lasers with wavelengths in the range of 325 to 425 nanometers.
The doping ratio of the guest material may be between 0.5% and 10%
and is selected to adjust various process parameters such as
patterning throughput and equipment parameters such as laser
intensity. For large area patterning, optical energy may be
delivered serially via scanning the laser using rotatable optical
elements. The laser used to transfer light energy to the solid
condensate may be aligned to the substrate and existing features by
any convenient and suitable method, including machine vision, and
making reference to fiducials, or readily referenced features on
the underlying substrate.
In another embodiment, thermal energy is delivered to the solid
condensate resist through absorption of light energy by the
substrate, which is converted to thermal energy and conducted to
the condensate resist. Light energy is delivered via a pulsed or
continuous wave laser. The wavelength of laser excitation is chosen
such that sufficient light absorption is achieved to result in
resist sublimation. For large area patterning, optical energy may
be delivered serially via scanning the laser using rotatable
optical elements. The laser used to transfer light energy to the
solid condensate may be aligned to the substrate and existing
features by any convenient and suitable method, including machine
vision, and making reference to fiducials, or readily referenced
features on the underlying substrate.
A microfeatured stamp 32 (FIG. 6A) defines parts of the resist mask
by raised portions 34 coming in contact with and subliming away
parts 36 of the mask (FIG. 6B). In this embodiment, thermal energy
is transferred through the direct or proximal contact with body
with a temperature higher than the condensate resist. The body,
hereafter referred to as the stamp 32, has patterned features,
providing a means to selectively transfer thermal energy and thus
selectively sublime the resist 36. The stamp may have two
dimensional raised features distributed over a large flat area,
such that it is brought into contact with the substrate to be
patterned one time for each resist patterning process step.
Alternatively, the stamp 32 may have two dimensional raised
features distributed over a large flat area which is less than the
area of the substrate 10 to be patterned, such that the stamp 32 is
brought into contact with the substrate to be patterned several
times for each resist patterning step, where the stamp is
translated between each contact process. Alternatively, the stamp
32 may have two dimensional raised features distributed over a
large curved area which is less than the area to be patterned such
as a cylindrical roller, so that the curved area of the stamp is
rolled over the substrate, such that contact between the stamp and
the substrate is maintained over the full condensate resist
patterning process. An additional support roller may be utilized to
provide counterbalancing force to limit substrate flexing.
The stamp 32 can be patterned by any convenient, and suitable means
and is reused over many patterning processes. As a result,
patterning methods which are slow, expensive, and high resolution
may be utilized, such as chemical etching through a
photolithographically defined resist, mechanical scribing with a
diamond stylus, direct laser ablation, or any other convenient and
suitable means. The stamp should have raised features of a height
equal to or greater than the thickness of the solid condensate,
such that only the raised features come into direct or proximal
contact with the substrate to be patterned in a desired way. Full
image transfer may be utilized by using a stamp with raised
features in direct correspondence to the desirably patterned film
features. Alternatively, incomplete image transfer may be utilized
by using a stamp with raised features that do not fully correspond
to the desirably patterned film features, such that,
inconsistencies in thermal energy transfer are accounted for to
result in the patterned film with dimensions true to designer
intent. The relative coverage of the raised features on the stamp
may be in a majority or a minority compared to the total stamp
area, depending on desired film duty cycle. The raised features may
be bounded, such that they are surrounded by lowered features.
Alternatively, they may not be bounded, such that the raised
features may extend to the edges of the stamping face. The aspect
ratio, or ratio of width or length to the height of the raised
features may cover a range from 0.1 to 10. The stamp may be
comprised of any convenient and suitable material. For high
throughput patterning, the stamp should be comprised wholly or
partially of high thermal conductivity materials, such as metals,
and specifically copper, stainless steel, chromium, or aluminum.
For dimensional stability, stainless steel or one of its alloys may
be utilized. For mechanical durability, the raised features may be
additionally coated with a thermally conductive layer with high
durability such as chromium, such that the stamp can be reused for
many patterning processes.
In particular, stamps may be of the form similar to those used for
rotogravure printing. In one method, cylindrical rollers used in
rotogravure are patterned using a pulsed Nd:yttrium aluminum garnet
laser of up to 500 watts in intensity to ablate the roller surface.
The beam diameter, pulse duty cycle, and beam profile of the laser
is modified to control the shape of the raised features. For
rotogravure, raised features may be minimum lengths and widths of 5
micrometers and typical heights of 1 to 40 micrometers. Aspect
ratios of raised features may be approximately 2. The cylindrical
roller for rotogravure may have lengths up to 5 meters, weigh up to
2000 kilograms and spin at up to 40 revolutions per second during
laser patterning, such that the cylinder is moving at a rate
greater than the laser. Unlike rotogravure printing, the stamp used
for patterning thin films is not filled with ink, so the dimensions
of the raised features may be dissimilar, in particular, their
aspect ratio and height. Rotogravure cylinders may be periodically
de-plated and re-patterned to ensure patterning fidelity.
The stamp used to transfer thermal energy to the solid condensate
may be aligned to the substrate and existing features by any
convenient and suitable method, including machine vision, and
making reference to fiducials, or readily referenced features on
the underlying substrate.
The substrate may be actively and uniformly cooled during
condensate resist patterning, such that temperature control and
dimensional stability are maintained and to provide a
counterbalancing thermal sink to limit total thermal power transfer
to the condensate resist. In order to limit resublimation of
patterned or unpatterned areas of condensate resist, the substrate
may be cooled to a temperature during the patterning process which
is lower than that for condensation and compression processes. This
lower temperature may be delivered, for instance, through
connection to cryostages cooled by open or closed cycle helium.
Depending on process speed, temperature, and pressure, it may be
preferred that the deposition chamber walls are also cooled and
thus coated with condensate resist to maintain substrate resist
integrity by reducing redeposition of sublimed resist and to aid
the cleaning of the chamber walls. Alternatively, an additional
large surface area cooled element could be integrated to prevent
sublimed resist redeposition.
Solid condensate resist patterning may occur in a variety of
environments, including inert gases such as nitrogen or argon, or
in vacuo. The environment may also include a partial atmosphere of
a gas which is the vapor form of the condensate resist in order to
equilibrate between sublimation and condensation to maintain
desired features in the resist. The low temperature of the
substrate may result in the undesirable condensation of gases other
than the resist material, so the environment may be preferably
absent of such impurities, such that levels or concentrations of
these gases are well below 1 part per billion. In particular, water
vapor may be desirable limited well below 1 part per billion.
In one embodiment, the patterning process is utilized to define
metals or organic semiconductor thin films for use in OLED
displays. A typical feature dimension for organic pixels or
sub-pixels for use in this application is approximately 10
micrometers to 250 micrometers in length and width and 1 to 200
nanometers in thickness. A typical feature dimension for metallic
electrodes, interconnections, or busing for use in this application
is approximately 10 micrometers to 100 centimeters in length and
width 1 to 500 nanometers in thickness. As such, the features which
are desirably transferred to the condensate resist may have
dimensions in the same range.
In one embodiment, the pattering process is utilized to define
metals or organic semiconductor thin films for use in OLED lighting
components. A typical feature dimension for organic pixels or
sub-pixels for use in this application is approximately 0.5 to 1000
centimeters in length and width 1 to 200 nanometers in thickness. A
typical feature dimension for metallic electrodes,
interconnections, or busing for use in this application is
approximately 10 micrometers to 1000 centimeters in length and
width and 1 to 500 nanometers in thickness. As such, the features
which are desirably transferred to the condensate resist may have
dimensions in the same range.
In one embodiment, the patterning process is utilized to define
metals or organic semiconductor thin films for use in organic
photovoltaic arrays. A typical feature dimension for organic pixels
or sub-pixels for use in this application is approximately 0.5 to
1000 centimeters in length and width 1 to 200 nanometers in
thickness. A typical feature dimension for metallic electrodes,
interconnections, or busing for use in this application is
approximately 10 micrometers to 1000 centimeters in length and
width and 1 to 500 nanometers in thickness. As such, the features
which are desirably transferred to the condensate resist may have
dimensions in the same range.
In one embodiment, the patterning process is utilized to define
insulating thin films for use as encapsulants. A typical feature
dimension for insulating layers for use in this application is
approximately 0.1 to 1000 millimeters in length and width and 1 to
100 micrometers in thickness. As such, the features which are
desirably transferred to the condensate resist may have dimensions
in the same range.
With reference to FIG. 7, partial-depth stamping leaves a uniform
thickness burn-off to remove the remainder of the desired regions.
Before burn-off is shown in FIG. 7A and after burn-off is shown in
FIG. 7B. In this embodiment, the selective sublimation of solid
condensate resist is followed by a uniform sublimation process. An
energy source that is uniform in nature sublimes a fractional
thickness of the solid condensate resist. This uniform sublimation
serves to ensure any desirably patterned condensate that
experienced incomplete sublimation may be completed. The uniform
sublimation will also remove the condensate resist from regions
that are desirably maintained. Because of this, the fraction of the
total condensate resist thickness that is removed does not exceed
50 percent. The uniform energy source for uniform sublimation may
include exposure to an element at an elevated temperature,
including the substrate support stage where energy may be
transferred by conduction, a uniform optical source where energy
may be transferred by radiation, a thermal point source which may
radiate thermal energy, or any convenient and suitable combination
of the preceding.
A substrate with a selectively patterned condensate resist layer
may be utilized to transfer the pattern to a subsequently deposited
film of conductor, insulator, or semiconductor material. The
desirably patterned film is deposited uniformly over the patterned
condensate resist.
FIG. 8 shows codeposition of materials (left) and deposition of a
single material (right) on to a substrate with a defined sublimable
mask. The desirably patterned film may be patterned by any
convenient and suitable means, including thermal evaporation,
sputtering, chemical vapor deposition, plasma deposition, or
physical vapor deposition. Uniform deposition may occur in a
variety of environments, including inert gases such as nitrogen or
argon, or in vacuo. The environment may also include a partial
atmosphere of a gas which is the vapor form of the condensate
resist in order to equilibrate between sublimation and condensation
to maintain desired features in the resist. The low temperature of
the substrate may result in the undesirable condensation of gases
other than the resist material, so the environment may be
preferably absent of impurities, such that levels or concentrations
of these gases are well below 1 part per billion. In particular,
water vapor may be desirably be limited well below 1 part per
billion.
Some methods of film deposition the utilization of a hot source.
For instance, thermal evaporation utilizes a hot source boat which
vaporizes a solid or liquid source material. The hot boat may
transfer thermal energy to the substrate by conduction or
radiation, which may be undesirably sublime the condensate resist
partially or entirely. In one embodiment, thermal baffles may be
utilized in the deposition chamber resist. The thermal baffles
utilized to block thermal transfer may be comprised of any
convenient and suitable materials, including metals which are
thermally connected heat sinks. In order to limit resublimation of
pattered areas of condensate resist, the substrate may be cooled to
a temperature during the deposition process which is lower than
that for condensation and compression processes. This lower
temperature may be delivered, for instance, through connection to
cryostages cooled by open or closed cycle helium.
In some instances, uniform sublimation of the condensate resist may
occur during the uniform disposition of the desirably patterned
film. In these cases, total resist sublimation is limited to less
than 50% of the total resist thickness in order to ensure high
device yield.
The geometric layout of the source may be any which is convenient
and suitable, including linear, point, or continuous. The
deposition direction may be vertical or horizontal and may occur on
top or bottom of the substrate. Simultaneous co-deposition of two
or more source materials is contemplated as well. The deposition
may take place in one or more chambers.
A variety of materials may be deposited depending on the device
which is being manufactured. The current invention is not meant to
be limited to use with certain materials. Some thin film device
components which may be deposited with the described processes
include electron and hole transport layers for OLED displays or
lighting components, emitting materials for OLED displays or
lighting components, device electrodes or OLED displays or lighting
components, interconnects and busbars for OLED displays or lighting
components, n-and p-type materials for organic photovoltaic
devices, device electrodes for OPV, interconnects and busbars for
OPV, and insulating thin films for encapsulants.
FIG. 9 shows pattering of a material by subliming the underlying
resist mask 40. The portions of the film on top of the masked
regions (FIG. 9A) are removed along with the resist material
leaving behind the patterned thin film 42 (FIG. 9B). To transfer
the pattern in the condensate resist to the desirably patterned
film, the condensate resist is lifted off. The direct solid to
vapor sublimation of the condensate resist lifts off the solid base
which supports a portion of the desirably patterned film, such that
it is removed from the substrate during resist lift-off.
Resist lift-off is effected by increasing the temperature of the
condensate resist across its sublimation point in
pressure-temperature space. This movement in pressure-temperature
space may be affected by an increase in temperature, a change in
pressure, or a combination of both. Uniform resist lift-off may be
achieved by any convenient and suitable means, including exposure
to hot gas, thermal heating conducted through the substrate
support, or thermal energy radiated by a distant localized source,,
such as, for instance, a hot filament. The change in pressure or
temperature may be temporally constant or follow a defined profile.
The quality of pattern transfer is observed to increase when
thermal heating is applied from the substrate, such as from a
heating element conducted through the substrate support.
It is preferred that the condensate resist layer be removed by, as
well as formed by, solid to vapor and vapor to solid processes,
respectively. Such enables an entirely dry deposition and removal
cycle that does not require liquids, limiting the need for solvent
disposal.
The quality of pattern transfer from condensate resist to film is
increased when sublimation is caused by an abrupt change in
temperature, such that the resist experiences a thermal shock. The
thermal shock may be delivered by any of the previously described
means.
In one embodiment, two condensate resists are utilized for film
patterning. The two resists are chosen to possess thermal expansion
coefficients that differ by at least 5%. By employing two
condensate resists, pattern transfer may be improved as when the
combination of thermal shock and differential thermal expansion
shears the resist film from the underlying substrate.
Substrate pre-cooling, resist condensation, resist compression,
resist patterning, film deposition, and resist lift-off may occur
in distinct processing chambers, where the temperature and
environment may be independently controlled. Alternatively, one or
more of the preceding process steps may occur in the same chamber,
such that total film patterning process throughput is increased.
The film patterning process may be employed one or more times, and
may take place in the same or a different set of chambers. Each
chamber may be separated by one or more doors, load locks, gates,
partitions, slit seals, or any combination and connected by a
substrate transfer system such as conveyor belts or rollers. The
substrate may be supported directly on components that additionally
provide substrate temperature control. The substrate may be
supported by any convenient means, such as magnetic bearings or
lateral force.
Substrate temperature may be monitored during any and all process
steps through the use of any convenient and suitable means,
including infrared machine vision, infrared sensors, and
thermocouples.
During thin film deposition, it is common for source material
utilization efficiency to be less than one hundred percent. Source
material which is not transferred to the substrate may be deposited
on the inside of the deposition chamber walls. This material may
grow in thickness over the course of many substrate coatings and
may eventually start to flake off and sourcing particulates and
dust, which may reduce functional device yield. As such, the
chamber must be cleaned periodically which has the undesirable
effect of reducing machine uptime. In one embodiment of the
invention, the deposition chamber is also coated with condensate
resist material and cooled to maintain resist integrity. The source
material lost to the inner chamber walls will thus be deposited on
the condensate resist. Periodically, the chamber may be heated such
that the resist is lifted off, providing a convenient means to
clean the inner chamber walls of the lost source material. This
process had the benefit of reducing the cleaning process time and
thus increasing machine uptime.
Resist that sublimes from the substrate may have a tendency to
redeposit on the substrate surface thereby obscuring features or
film quality. A large surface area, cryogenically cooled surface
near the substrate such as a coldhead, shield or fin may be
provided to collect resist that otherwise would have been
redeposited on the substrate.
FIGS. 10-13 show the results of experiments utilizing sublimable
carbon dioxide masks. These figures illustrate the efficacy of the
invention disclosed herein.
* * * * *